No hot water — what's wrong with the water heater?
The first question, before anything else: is your heater electric or gas? The answer changes this whole page. Electric heaters have safe steps you can do yourself. Gas heaters — we give no DIY steps at all.
The problem
Water runs cold or only lukewarm; or it's hot for a few minutes and then goes cold; or you hear rumbling and popping from the tank; or the hot water is discoloured or smells; or the breaker trips every time the heater switches on.
Likely causes
The thermostat is set low or has failed (electric)
The simplest cause and the first thing to check. It may simply be set too low, or it may have failed so it never switches the element on at all. The right setting is around 60°C.
A burnt-out heating element
If your tank has two elements and one has burnt out, you get lukewarm water, or hot water that disappears very quickly. The part is cheap, but replacing it means draining and opening the tank — doable for a careful DIYer, provided the power is fully off.
Limescale in the bottom of the tank
In hard-water areas, scale settles over the element and insulates it from the water. The result: rumbling and popping, weak heating, and a higher electricity bill. An annual drain-and-flush prevents it.
The reset button has tripped
Most electric heaters have a small red thermal-cutout button behind the access panel. If it's tripped, the heater is dead. One press may bring it back — but if it trips again, something is genuinely wrong and you need a technician.
A worn-out anode rod
A magnesium rod that corrodes instead of your tank. If it's never been changed, the tank itself starts to rust — the tell is yellowish water or a foul smell. Replacing it is far cheaper than replacing the tank.
Gas burner or ignition (gas heaters)
Pilot out, faulty ignition, or a failed gas valve. Do not attempt any of it — see 'when to call a professional' below.
Fix it — step by step
- Identify what kind of heater you haveThick electrical cable and a dedicated breaker → electric, carry on. A gas pipe and a burner → gas: stop here and call a gas technician. This page gives no DIY steps for gas heaters.Not sure? Assume gas and call someone. Caution is free.
- Kill the heater's breaker completelyAt the main panel, not just the wall switch. Confirm it's actually dead (flip the wall switch — nothing should happen).A cheap non-contact voltage tester confirms the power really is off. Don't trust the breaker label alone.
- Check the reset buttonUnscrew the small metal access panel on the heater body. Behind it you'll find a small red button. If it's popped out, press it until it clicks.If it trips again within days — don't press it a third time. There's a real fault (thermostat or element) and it needs a technician.
- Check the thermostat settingBehind the same panel is a dial or an adjustment screw. Set it to about 60°C. Higher raises the scald risk and speeds up scaling.60°C is the sweet spot: hot enough to stop bacteria, not hot enough to scald.
- Drain the tank and flush the scale outClose the cold-water inlet valve. Attach a hose to the drain valve at the bottom of the tank and run it to a drain. Open a hot tap somewhere in the house (this breaks the vacuum), then open the drain valve.Let it run until the water is clear. The first of it will be cloudy with white grit — that grit is your problem.
- Refill the tank — in the right orderClose the drain valve, open the cold inlet, and leave that hot tap open until water flows steadily with no spitting air. Only then close it.⚠️ Never switch the power back on with the tank empty or half-full — the element burns out in seconds. Confirm it's completely full first.
- Restore power and waitTurn the breaker on and wait 30-60 minutes depending on tank size. Then run a hot tap and test.If it heats now, it was the scale or the reset. Flush it annually and it won't come back.
- Still cold? Gather the facts for the technicianAlways lukewarm = one of two elements burnt out. No heat at all = thermostat, element or supply. Hot water that runs out fast = the lower element.Tell the technician what you did and what happened. It saves you the diagnostic fee.
Tools & parts you'll need
Disclosure: some parts links above are affiliate links — if you buy through them we may earn a small commission from the store, at no extra cost to you. It does not change which parts we recommend.
When to call a professional
Stop and call a professional immediately if: your heater runs on gas (every case, no exceptions); water is leaking from the body of the tank itself (it's rusted through from inside — that's a replacement, not a repair); the T&P safety valve is releasing water or steam; the breaker trips whenever the heater runs (an earth leak — shock risk); or you are simply not comfortable opening a panel with mains voltage behind it. That last one is entirely legitimate: nothing on this page is worth an electric shock.
Need a pro? We'll point you to one.
AskFix takes no commission and books nothing — we give you a technician's number and you call them directly.
AskFix is not a broker or a marketplace. We take no commission on any work you agree with a technician, and we do not warrant their work — the agreement is directly between you and them.
Not sure what's broken? Take a photo.
Snap a photo with your phone — AskFix identifies the appliance, reads the model plate, and tells you what's wrong and how to fix it. Free, no sign-up.
Try photo diagnosisPeople also ask
What's the rumbling and popping noise from the tank?
Limescale on the bottom. Water gets trapped under the scale layer, boils, and escapes as noisy bubbles. Not immediately dangerous, but it means the heater is burning extra electricity and shortening its own life. Drain and flush it.
How often should I drain a water heater?
Once a year — and every six months in hard-water areas. It's the cheapest preventive maintenance in the entire house.
The hot water runs out very quickly
Most common cause: the lower element has burnt out, so the tank only heats its top half. Second: heavy scale has eaten the tank's usable volume. Third: a failed mixing valve blending cold into the hot.
The hot water is yellow or smells bad
Yellow = rust, usually meaning the anode rod is spent and the tank has started corroding. A rotten-egg smell = bacteria reacting with the anode. Replacing the anode addresses both — and it's far cheaper than a new tank.
What temperature should I set it to?
60°C. Below 55°C lets legionella bacteria grow in the tank. Above 65°C accelerates scaling and makes tap water hot enough to scald skin in seconds — a real risk with small children.
Water is dripping from a small valve next to the heater
That's the T&P (temperature & pressure) safety valve. An occasional drip after heating can be normal, but a steady leak means either the system pressure is too high or the valve has failed. Never cap it or plug it — it is the valve that stops the tank exploding. Call a technician.